Clark's crushing the coal into a diamond is a homage to the many times Superman has done this in the comic series, as well as Superman III (also for Lana, played by Annette O'Toole) and in the 1950s Superman series Adventures of Superman, in an episode called 'Jungle Devil'. Also the Arrowverse's Clark Kent AKA Superman played by Tyler Hoechlin crushed coal into a diamond to propose to his Lois Lane played by Elizabeth Tulloch during the "Elseworlds" Episode of Supergirl. They both appear alongside Tom Welling's Clark Kent during the Batwoman Hour of "Crisis On Infinite Earths".
The 100th episode in the series.
Equal top rated episode of the series with Episode 200 (S10E04).
This is the only episode that shows what happens during the transition from the cave to the Fortress when Clark puts the Key into the Kawatche cave table.
When Clark shows he knows everything that will happen in the near future, Chloe calls him "McFly". This is a reference to the Back to the Future trilogy in which the main character Marty McFly travels through time. Marc McClure, who plays Dax-Ur and Jimmy Olsen in the Christopher Reeve Superman movies played the role of Dave McFly in the first and third installment of the trilogy.